Encoder Readhead Error Correction for Absolute Position Scales
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Solution Overview
Problem
Existing incremental encoders with embedded absolute position information suffer from degradation in position measurement performance due to the removal of too many adjacent scale lines, limiting the maximum scale length and reducing the number of unique absolute codewords.
Innovation Solution
A readhead that captures a snapshot image of an encoder scale with embedded absolute position information, using an incremental position extractor to calculate a global phase value while applying error correction for sensor element variations and distortions, and an absolute position extractor to identify embedded features, enhancing measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If too many adjacent scale lines are removed from the encoder scale to embed absolute position information, then the number of unique absolute codewords increases, but the position measurement performance degrades
Solution Approach 1:
The patent applies error correction parameters to compensate for the degradation in position measurement performance caused by removing scale lines. By adjusting and correcting measurement parameters, the system maintains high measurement precision while embedding absolute position information through removed scale lines.
Solution Approach 2:
The patent implements feedback mechanisms that detect and correct measurement errors in real-time. The system continuously monitors position measurement performance and applies corrections based on detected deviations, ensuring that the removal of scale lines for encoding absolute position does not compromise overall measurement accuracy.
2Loss of information
If too many adjacent scale lines are removed from the encoder scale, then more absolute codewords can be embedded, but the maximum possible scale length is reduced
Solution Approach 1:
The patent uses parameter changes to optimize the balance between codeword capacity and scale length. By modifying measurement and encoding parameters, the system achieves higher absolute position resolution without proportionally reducing the usable scale length, thereby resolving the contradiction between embedding capacity and physical scale dimensions.
3Measurement precision
If error correction is applied to account for sensor element variations, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The patent implements feedback-based error correction that automatically compensates for sensor element variations. The system measures actual performance deviations and applies corrective transformations, achieving high measurement accuracy without requiring overly complex manual calibration or adjustment mechanisms.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Improves measurement accuracy by mitigating errors from sensor variations and distortions, allowing for precise determination of both incremental and absolute positions with higher resolution.
Implementation Method 1
an image sensor comprising a plurality of sensor elements for capturing a snapshot image of a portion of the encoder scale
Implementation Method 2
capturing a snapshot image of a portion of the encoder scale
Data Source
AI summary
A readhead that can read an encoder scale having a series of scale markings arranged in a periodic pattern and embedded scale features that encode absolute position information, including an image sensor for capturing a snapshot image of a portion of the encoder scale and a position analyser for determining a position of the readhead relative to the encoder scale from the image. An absolute position extractor extracts absolute position information from the embedded scale features in the image. An incremental position extractor generates a global phase value describing incremental position by analysis of the pattern of scale markings in the image, and is configured to apply an error correction when calculating the global phase value to account for variations in the contribution to the value from different sensor elements of the image sensor. Also, an encoder apparatus including a combination of the readhead and the associated encoder scale.